Presently, many convenience stores and service stations are of the "self-service" type, which contain dispensers for dispensing fuel products, such as gasoline or kerosene, upon the request of a customer. These stations typically have a number of fuel dispensers so that more than one customer may be serviced at a time. In addition, each of the dispensers typically includes a number of nozzles which are each connected to a separate fuel storage tank, or else includes a single nozzle with access to more than one fuel storage tank in order to dispense a number of different fuel products. To operate the dispenser, a customer activates an on/off lever or a start button to enable fuel to flow from the designated underground tank, through a fuel line, to the dispenser, and out the nozzle to a waiting vehicle or container.
At these types of refueling stations, there is typically a single control panel for controlling the operation of all of the dispensers at the station. This panel is typically operated by a station attendant from the interior of the station or store. This panel may contain controls for setting and clearing the dispensers, as well as registering the amount of fuel dispensed from each dispenser.
One problem that has arisen with these multi-dispenser service stations is that when a single dispenser requires servicing, or in the case of an accident such as a dispenser being struck by a vehicle, isolation and shut-down of all power to the individual malfunctioning or damaged dispenser cannot be accomplished without also shutting down the power to the rest of the dispensers at the station. A complete shut-down of the station, even for short periods of time, is very undesirable since during the shut-down period no fuel sales and thus no revenue generation can occur. However, by law, all fuel dispensing stations are required to have an emergency shut-off system for immediately disconnecting power to a damaged or malfunctioning dispenser in order to eliminate the risk of fire or electric shock. Without a mechanism to isolate and separately shut-off an individual dispenser, the only way to satisfy this requirement and safely repair a damaged dispenser is to shut-down all power to all of the dispensers, thus rendering the entire station inoperable.
In the past, emergency shut-down systems were primarily mechanical and relied upon mechanical switches to break the power connections to the fuel dispensers. More recently, emergency shut-off systems have been developed wherein a single stop switch with annunciator is attached to the station control panel to provide for a true isolation of all of the fuel dispensers in the case of an urgent situation at the pumps. In these types of systems, which operate on DC power, relays rather than mechanical switches are used to break the AC connections to the dispensers, thereby disconnecting the power to the dispensers. While these systems are beneficial in that they enable the emergency stop to be activated directly from the station control panel, they too have a number of problems. In particular, these systems still require that all of the dispensers at a particular station be shut-down in order to disable a single dispenser, even if only one dispenser is damaged or in need of servicing.
To avoid the financial consequences of a complete station shut-down when only a single dispenser needs repair, some station operators have resorted to disabling a breaker for the targeted dispenser to disable power to that dispenser. However, this practice is risky, since it may be difficult to determine whether the correct breaker has been disabled. Further, it may be possible for backfeed power from the underground pumps for the fuel tanks to migrate back to the supposedly "isolated" dispenser, when another dispenser connected to that same tank is operated, creating, a hazardous situation.
Thus, a need exists for a lock-out, tag-out, true isolation system for a fuel dispensing facility which enables not only the emergency shut-down of all of the dispensers at the facility, but also the isolation and shut-off of power to each dispenser individually, so that an individual dispenser can be shut-down for service or repair without interrupting the operation of the rest of the station.